FIELD OF THE INVENTION
The invention relates to a superconductor structure having a substrate, at least one buffer layer which has been deposited on the substrate, and a layer of a metal oxide superconductor material with a high critical temperature which has been deposited on the buffer layer, the substrate including a glass material which is sufficiently temperature-resistant to be able to withstand the maximum temperature during production of the buffer layer and the superconductor layer. The invention also relates to a current limiter device and a process for producing a corresponding superconductor structure. A structure and a corresponding production process of this general type can be found in "Physica C", Vol. 267, 1996, pages 355 to 360.
Superconductive metal oxide compounds with high critical temperatures T.sub.c of over 77 K are known, and these compounds are therefore also known as high T.sub.c superconductor materials or HTS materials and, in particular, enable an LN.sub.2 (liquid nitrogen) cooling technique to be used. Such metal oxide compounds include, in particular, cuprates of special material systems, for example of the Y--Ba--Cu--O or Bi--Sr--Ca--Cu--O types, in which the Bi component can be partially substituted by Pb. There can be a plurality of superconductive high T.sub.c phases within individual material systems, which phases differ through the number of copper-oxygen lattice planes or layers within the crystalline unit cell and have different critical temperatures.
It is desired for these known HTS materials to be deposited on different substrates for different applications, the aim generally being to form pure-phase superconductor material as far as possible. For example, metallic substrates are provided in particular for conductor applications. Furthermore, DE 195 20 205 A describes the general use of substrates made from glass material as supports for conductor tracks made from HTS material in current limiter devices. In order to allow textured growth of the HTS material, it is also known for a suitable buffer layer to be applied to that surface of the substrate which is to be coated with the HTS material.
The production of a biaxially oriented thin film made from the HTS material YBa.sub.2 Cu.sub.3 O.sub.7-x on various glass substrates is described in the literature reference from "Physica C" which was mentioned in the introduction. Materials with a coefficient of expansion .alpha. of at most 4.6.times.10.sup.-6 .degree. C..sup.-1 were used for the glass substrate used in that document. These materials are so-called "hard glass", since glass materials with .alpha. values of below 6.times.10.sup.-6 /K are generally referred to in this way, while glass materials with a .alpha. value above this are referred to as "soft glasses" (see H. G. Pfaender: "Schott-Glaslexikon", 1984, page 30). Moreover, the substrates of the known structure had a very small surface area to be coated, which was covered with oriented, Y-stabilized ZrO.sub.2. However, it has emerged that with the known structure it is only possible to achieve critical current densities J.sub.c of the order of magnitude of 10.sup.4 A/cm.sup.2 (in the zero field). Current densities of this level are regarded as being too low for many applications.